For things like notes on a play, in my own copy of a text, I think noting in the actual book next to the original text is unbeatable as everything is unlosably together. Post its can fall out or get stuck on the wrong page but are good to mark passages needed to construct an essay.

Edit.

I also have a couple (or perhaps a few more) of local history books and I have annotated some pages to add family details, such as 'my father was born in this house'. Again, I feel that the additional information belongs in the book.

'Major Bigglesworth' said Von Stalhein coldly, 'there are times when I seriously wonder if you were created by the devil just to annoy me.'

If I've got a ring-bound copy (ie copy of copy) of something factual, I might make notes on the pages, or if it is work-related updates and corrections. In the latter case it might be the only hard copy, and becomes our 'working document'Real and proper books- no way!

'....you cannot flout Nature with impunity. Treat Nature with respect, and she will tolerate you, even encourage you; but treat her with contempt, and your days are numbered.'Hits the Trail

It depends on the book. Some of my textbooks definitely have added notations in pencil, because I find that useful and pertinent and ultimately time-saving (particularly if I've noted another reference to pursue). But in good quality novels (and Biggles definitely rates in that category ) I would not add notes.

I do not turn the corners of the pages - probably because I was taught not to as a child - and still find I can get something of a slight thrill when I open an old book at a book-marked section and as I begin reading, realise why I found it interesting enough to place the bookmark in.

I do become seriously annoyed when I borrow books from my college library and discover that some inconsiderate person has written their notes in the margins. That's defacing a book that is not one's own property. I always p/copy the relevant sections and then I can scribble over them to my heart's content.

I think it's okay to put notes in margins of text books, as long as the books belong to you. They are working book, tools of the trade, designed to assist, and I find scribbled notes in the margins at the appropriate place helps enormously. I have even been known to highlight passages. what n I took my degree I bought second-hand books, because money was tight. These had markings, scribbles and highlights and in a couple of instances, actually helped to draw attention to a point I'd missed.

The Decision to Survive - A good pilot is both born and made. The best would look upon his work as a combination of adventure and a serious mission. – Major General Sir Frederick Sykes